SFR vs. for our sample and additional galaxies from the literature. As discussed in Sect. 2.2, we include I Zw 18 as one of our sample galaxies (see also Schruba et al. 2012). The open triangles for Schruba et al. (2012) correspond to their compilation of literature data and the filled ones to their metal-poor dwarf observations. CO non-detections are shown by leftward arrows. The rightmost regression line corresponds to the linear correlation found by Gao & Solomon (2004), and the leftmost one to our new determination, also compatible with a slope of unity (see text). The horizontal dotted line gives the IR luminosity limit above which the linear LIR- correlation of Gao & Solomon (2004) no longer holds.